Gaseous discharge device with shield for directly heated cathode



g- 30, 1966 w. E. BAILEY, JR.- ETAL 3,

GASEOUS DISCHARGE DEVICE WITH SHIELD FOR DIRECTLY HEATED CATHODE FiledJuly 10, 1961 I TANTALUM TAN/UM INVENTORIS:

WARD E. BAILEY,JR. WlLLlAM J. KEARNS,

BY, TH IR ATTORNE United States Patent 3,270,232 GASEOUS DISCHARGEDEVICE WITH SHIELD FOR DIRECTLY HEATED CATHODE Ward E. Bailey, lira,Pittsfield, Mass., and William J. Kearns, Scotia, N.Y., assignors toGeneral Electric Company, a corporation of New York Filed July 10, 1961,Ser. No. 123,024 7 Claims. (Cl. 313-38) This invention relates togaseous electric discharge devices and pertains more particularly to anew and improved ceramic and metal thermionic cathode gas diode.

In many circuit applications, such, for example, as power generatorcircuits, it is desirable to employ a gaseous rectifier diode.Additionally, it is often desirable to employ such circuits inequipment, such as high speed vehicles, wherein the circuits, includingthe diode, are normally subjected to substantial mechanical shock andvibration as well as wide circumambient temperature ranges includingsubstantially high temperatures.

In applications of the above-discussed types it is desirable that thediode be adapted for withstanding, over an extended operating tube life,the normally encountered conditions of shock and vibration.Additionally, it is desirable that the devices be adapted for operatingover the whole of the normal ambient temperature range with stableelectrical characteristics including a substantially low forwardpotential drop, and substantially constant tube potential drop eachconducting cycle and for all values of tube current. It is alsodesirable that the diodes be adapted for operating with constantfilament power over the entire normal ambient temperature range thusobviating the need for filament derating.

Further, in constructing electric discharge devices of the presentlyconsidered types it has been found desirable to fabricate certaindifferent parts of certain different materials in order to takeadvantage of various desirable properties thereof, such, for example, ashigh refractoriness and effectiveness as a base for an emissivematerial. However, at elevated temperatures some of such differentmaterials are generally chemically incompatible in the sense that theytend readily to alloy and adversely affect the structures in which theyare employed. Therefore, it is desirable to provide arrangements whichwill allow the use of such different materials in close association butwithout the danger of adverse effects and subsequent tube inoperabilityresulting from the usual incompatibility of the materials.

Disclosed and claimed in copending US. application S.N. 123,023 of W. J.Kearns, filed concurrently herewith and assigned to the same assignee asthe present invention, and now US. Patent 3,204,140, is a ceramic andmetal thermionic cathode gas diode and method of manufacturing sameadapted for affording the above-discussed desiderata. The presentinvention contemplates the provision of a modified form of diode adaptedfor affording the above-discussed desiderata and for ensuring againstadverse effects resulting from chemical incompatibility of certainmaterials employed in the manufacture of the devices. More specifically,the present invention contemplates the provision of an improved ceramicand metal thermionic cathode gaseous diode which is in an alternativeform of device for attaining the functions of the device disclosed andclaimed in the above-mentioned copending Kearns application and whichcomprises a highly mechanically damped electrode system and thus isparticularly adapted for withstanding substantial mechanical shock andvibration. Additionally, the present invention, as does theabove-mentioned Kearns invention; contemplates structure effective forproviding a device adapted for operating with the above-discussedelectrical operat- Patented August 30, 1966 'ice ing characteristicsover the whole of a circumambient temperature from about 65 C. to about+400 C. The present invention also contemplates an electrode arrangementhaving nickel-containing elements effectively isolated from certaintitanium elements which can be adversely affected thereby.

Accordingly, a primary object of the present invention is to provide anew and improved ceramic and metal thermionic cathode gaseous rectifierdevice.

Another object of the invention is to provide a new and improved ceramicgaseous electric discharge device adapted for substantially uniformoperating characteristics over a substantially wide normal operatingtemperature range including relatively high temperatures.

Another object of the invention is to provide a new and improved ceramicand metal gaseous electric discharge device adapted for operating withsubstantially uniform electrical operating characteristics at.relatively high circumambient temperatures and without the need for anycathode derating.

Another object of the invention is to provide a ceramic discharge devicesystem including both titanium and nickel parts and improved means foravoiding adverse effects on the titanium parts by the presence of nickelin the device.

Further objects and advantages of the invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize the invention will be pointed out with particularity in theclaims annexed to and forming part of this specification.

In carrying out the objects of the invention there is provided a ceramicand metal gaseous discharge device including an envelope'comprising apair of cylindrical ceramic insulators, and a titanium washer-likemember buttsealed between the opposed ends of the insulator and atitanium disk-like member butt-sealed to the outer end of each insulatorto complete the envelope. The disk-like member at one end of theenvelope comprises a planar anode while the disk-like member at theother end and the washer-like member constitute contacts of a directlyheated nickelate cathode. The cathode is a nickelate-impregnated nickelwire mesh ribbon-like construction formed generally in the shape of an Sand extending parallel to the longitudinal axis of the envelope. Theannular cathode contact member includes an inner rim portion disposedinteriorly of the tube envelope. One end of the cathode is secured to adiscrete support rod which extends parallel to the axis of the tubeenvelope and is supported by and electrically connected to the inner rimpor tion of the annular contact member. The other end of the cathode issecured to a second discrete support rod which includes a steppedsection disposing the major length of the rod on the longitudinal axisof the envelope. This rod is electrically secured to the lower disk-likemember. The support rods are formed of a material which is non-alloyingat the operating temperature with the titanium in the tube structure.Also carried on the inner rim of the annular contact member is arefractory metal shield surrounding the cathode and extendingconcentrically in the envelope in close proximity to the cathode andeffective for providing uniformity of temperature of the cathodethroughout the axial length thereof.

For a better understanding of the invention reference may be had to theaccompanying drawing wherein:

FIGURE 1 is an enlarged elevational sectional view of a gaseousdischarge device with preferred materials constructed according to thepresent invention; and

FIGURE 2 is a transverse sectional view taken along the lines 2-2 inFIGURE 1 and looking .in the direction of the arrows.

Referring to FIGURE 1, there is illustrated a gaseous discharge devicecomprising an embodiment of the present invention and generallydesignated 10. The device includes a ceramic and metal envelope 11 whichcontains an inert gas, such as Xenon, at approximately 100 microns ofpressure and comprises coaxially arranged upper and lower cylindricalceramic insulators or wall sections 12 and 13, respectively, and upperand lower metal end caps or disk-like members 14 and 15, respectively.Each of the end caps 14 and 15 includes on its inner side an annularshoulder 16 which is dimensioned to extend into the corresponding end ofthe respective ceramic wall section 12 or 13. This arrangement serves tofacilitate assembly of the tube envelope sections and to insureconcentricity thereof. Also included in the envelope structure is anannular of washerlike contact and electrode support member 17 which isinterposed between the opposed ends of the insulators 12 and 13. Eachside of the member 17 is formed to include a shoulder 16 for extendinginto the opposite ends of the ceramic sections 12 and 13. This featurealso is adapted for facilitating stacking of the parts and assembly ofthe tube as well as concentricity of the parts in the finished envelope.

The metal members 14, 15 and 17 are preferably formed of titanium.However, the present invention is operative if zirconium replaces thetitanium in whole or in part. The insulators 12 and 13 are formed of asuitable ceramic which is adapted for matching the thermal expansion oftitanium and thus facilitates bonding thereto and subsequent use of thedevice at varying temperatures without adversely affecting the ceramicof the bonds between the ceramic and metail members. A group of ceramicsfound to be suitable are generally known in the art and available underthe denomination Forsterites. One such Forsterite is disclosed andclaimed in US. Patent No. 2,912,340 of A. G. Pincus issued November 10,1959, and assigned to the same assignee as the present invention.Another ceramic which is particularly suitable for use in constructingthe present device is the Forsterite-Spinel disclosed and claimed incopending U.S. application S.N. 831,510 of R. H. Bristow, filed August4, 1959, now Patent No. 3,060,040, and assigned to the same assignee asthe present invention.

The ceramic and metal members are suitably joined by butt-sealsindicated by the heavy dark lines 18 to complete the envelope structure11 by metallic bonds which are preferably formed by the method disclosedand claimed in U.S. Patent No. 2,857,663 of J. E. Beggs issued October28, 1959, and also assigned to the same assignee as the presentinvention. It is understood that in some applications other sealingtechniques are equally applicable such, for example, as any one of theseveral generally known methods requiring premetalizing of the ceramicand the use therewith of a solder material to effect bonds between themetallized ceramic surfaces and another member. However, the bondingmaterial employed preferably should be characterized by low oxygenpermeability and a low evaporation rate. Thus, for example, solderscontaining silver would be undesirable because of oxygen permeationespecially at elevated temperatures. Thus, the seals are preferablysilver-free. This feature, however, does not constitute part of thepresent invention but is disclosed and claimed in the above-mentionedcopending Kearns application. Gold-containing solders would be ofmarginal utility because of their high evaporation rate during thesealing process which would tend to cause deposition of conductivematerial on the insulator walls. The abovementioned sealing techniquedisclosed in the Beggs patent and which involves the use of titanium hasbeen found particularly effective in the manufacture of the tubeillustrated.

In the completed envelope 11 the upper disk-like member 14 serves as aplanar anode, the lower member 15 serves both as a cathode supportelement and a cathode contact member. The annular contact member 17 alsoserves the dual functions of cathode support and cathode contact.Additionally, the member 17 includes an inner rim portion 18 whichserves several functions, one of which is to provide partial support fora cathode structure generally designated 20 which will now be describedin detail.

The cathode structure 20 is of the directly-heated type and comprises anickel wire mesh element 21 in the form of a substantially wide ribbonand impregnated with nickelate. The nickelate cathode is employed due toits normal high operating temperature which permits substantialelevation of the temperature of the envelope without adversely affectingoperation of the cathode or requirement of filament derating. Thisconcept is also disclosed and claimed in the copending Kearnsapplication. The mesh 21 is in generally sheet or ribbon form so as tohave substantial width and thereby serve as a copious and relativelyrigid source of electrons. Additionally, and as seen in FIGURE 2, themesh is generally S-shaped with the center thereof on the axis of theenvelope 11. One end of the S-shaped cathode mesh is suitably secured toa discrete refractory metal filament support rod 22. The rod 22 iseccentric and parallel relative to the axis of the envelope and includesa transversely extending foot portion 23 electrically secured, as bywelding, to the rim portion 19 of the contact member 17. The other endof the cathode mesh 21 is suitably secured to a second discreterefractory metal filament support rod 24. The rod 24 includes aninwardly extending stepped section 25 which disposes the lower sectionof the rod on the axis of the tube envelope. A foot portion 26 of therod 24 is welded to the lower end cap 15 and thus is electricallysecured thereto.

In the described cathode support structure the rods '23 and 24 areformed of tantalum or any other highly refractory material which is notreadily alloyable with titanium. Thus, the nickel-containing cathode isisolated and prevented from alloying with the titanium of which thecontact members '15 and 17 are formed. Additionally, the support rodmounting arrangement and the relatively wide ribbon-like and S-shapedcathode provides for a highly-damped directly-heated cathode systemadapted for withstanding substantial mechanical shock and vibration. Infact, the disclosed structure has been found effective for withstandingmechanical shock of 50 gs and vibrations of 20 gs throughout the rangeof from 10 to 2000 c.p.s. across the operating ambient temperature rangeof from 65 C. to +400 C.

In the just-described arrangement the inner rim portion 19 of theannular contact member 17 serve-s additionally as means for shieldingthe ceramic insulator 13 from deposition thereon of conductive material.Specifically, the central aperture in the annular contact member 17 isso dimensioned that the inner rim 19 extends substantially inwardly andthus shields the lower ceramicto-metal bonds from any conductivematerial that may be sputtered from the cathode.

The upper insulator .12 is shielded from deposition thereon ofconductive material by a refractory metal tubular shield 27 which canadvantageously be formed of molybdenum. The shield 27 is preferablycylindrical and is secured concentrically in the envelope to the uppersurface of the inner rim portions 18 of the member 17 by a plurality ofcircumferentially spaced tabs 28 Welded between the shield 27 and themember 17. The upper end of the shield 27 extends in close proximity tothe anode :14 and thus shields substantially all of the upper insulatorfrom deposition of sputtered material originating from the cathode whichis spaced inwardly from the outer end of the shield.

Additionally, the shield 27 extends in close proximity to the cathodemesh 21 along the whole axial length of the mesh. Thus, the shield 27serves to maintain a substantially uniform temperature and emissivitythroughout the axial length of the cathode.

In order to facilitate connecting the described device in a circuit, thevarious contact elements are each provided with a radially protrudingapertured tab or terminal 29. Additionally, the cathode contact 15 isformed with an integral threaded nut 30 which includes opposed flattenedland surfaces 31 for accommodating a wrench and enabling the device tobe affixed to a support surface carrying a threaded mounting stud (notshown). Thus, the device may be mounted rigidly and easily on, forexample, the chassis of a piece of equipment and will provide fordesirable high heat transfer from the tube to the relatively moredissipative chassis.

The described tube structure is preferably manufactured according to themethod disclosed and claimed in the above-referenced copending Kearnsapplication.

While a specific embodiment of the invention has been shown anddescribed it is not desired that the invention be limited to theparticular forms shown and described, and it is intended by the appendedclaims to cover all modifications within the spirit and scope of theinvention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A ceramic and metal gaseous discharge device comprising an envelopeincluding a pair of coaxial ceramic insulators, a pair of disk-likecontact members sealed across the outer ends of said insulators, one ofsaid disk-like members comprising an anode and the other a cathodecontact, an annular contact member sealed between said insulators andincluding an inner rim portion disposed concentrically in said envelope,a tubular open-ended metallic shield supported on said inner rim portionof said annular member and extending concentrically in said envelope toa point adjacent said anode, a directly heated cathode disposed in saidshield, a discrete first lead supporting one side of said cathode andmounted on and conductively connected to said rim portion of saidannular contact member, and a discrete second lead supporting the otherside of said cathode and extending through said annular contact memberand mounted on the inner surface of the disk-like member comprising acathode contact.

2. A ceramic and metal gaseous discharge device according to claim 1,wherein said cathode comprises a wire mesh impregnated with an electronemissive material and extends parallel to the longitudinal axis of saidenvelope.

3. A ceramic and metal gaseous discharge device according to claim '1,wherein said cathode is in sheet form, is generally S-shaped and extendsparallel to the longitudinal axis of said envelope.

4. A gaseous discharge device according to claim 1, wherein said cathodeis in general sheet form and generally S-shaped with the center thereoflying on the axis of said envelope, one of said support rods iseccentrically disposed and is secured electrically to said rim portionof said annular contact member, and the major portion of the other ofthe said support rods lies on the axis of said envelope and is securedelectrically to said disk-like member comprising a cathode contact.

5. A ceramic and metal gaseous discharge device according to claim 1,wherein said cathode is a nickel wire mesh impregnated with nickelate.

6. A ceramic and metal gaseous discharge device according to claim 1,wherein said contact members are substantially titanium and said cathodecontains nickel and is supported on rods of a metal which issubstantially non-alloying with titanium at the operating temperature ofsaid device.

7. A ceramic and metal gaseous discharge device comprising an envelopeincluding a pair of coaxial ceramic insulators, a pair of titaniumdisk-like contact elements sealed across the upper ends of saidinsuiators, one of said disk-like elements constituting an anode and theother a cathode contact, a titanium annular contact member sealedbetween said insulators and including a substantial inner rim portiondisposed .interiorly of said envelope, a directly-heated cathodecontained in said envelope and of a substantially wide nickel wire meshribbon which is impregnated with nickelate, is generally S-sh-aped andextends parallel to the axis of the said envelope with the centerthereof on said axis, an eccentrically located discrete first supportrod having one end of said cathode electrically secured thereto andbeing electrically secured to said rim portion of said annular contactmember, a discrete second support rod having the major portion thereofextending along the axis of said envelope and having the ends thereofelectrically secured to the other end of said cathode and said cathodecontact, said support rods comprising a metal which is substantiallynon-alloying with titanium at the operating temperature of said device,and a tubular open-ended refractory metal shield mounted concentricallyabout said cathode in close proximity thereto and supported on saidinner rim portion of said annular contact member, said shield extendingin close proximity to said cathode throughout the axial length of saidcathode and said shield cooperating with said anode in defining a voidspace therebetween.

References Cited by the Examiner UNITED STATES PATENTS 1/1949 Smith3l3-205 X 8/1960 Riley et al. 313-497 X C. R. CAMPBELL, D. E. SRAGOW,

Assistant Examiners.

1. A CERAMIC AND METAL GASEOUS DISCHARGE DEVICE COMPRISING AN ENVELOPEINCLUDING A PAIR OF COAXIAL CERAMIC INSULATORS, A PAIR OF DISK-LIKECONTACT MEMBERS SEALED ACROSS THE OUTER ENDS OF SAID INSULATORS, ONE OFSAID DISK-LIKE MEMBERS COMPRISING AN ANODE AND THE OTHER A CATHODECONTACT, AN ANNULAR CONTACT MEMBER SEALED BETWEEN SAID INSULATORS ANDINCLUDING AN INNER RIM PORTION DISPOSED CONCENTRICALLY IN SAID ENVELOPE,A TUBULAR OPEN-ENDED METALLIC SHIELD SUPPORTED ON SAID INNER RIM PORTIONOF SAID ANNULAR MEMBER AND EXTENDING CONCENTRICALLY IN SAID ENVELOPE TOA POINT ADJACENT SAID ANODE, A DIRECTLY HEATED CATHODE DISPOSED IN SAIDSHIELD, A DISCRETE FIRST LEAD SUPPORTING ONE SIDE OF SAID CATHODE ANDMOUNTED ON AND CONDUCTIVELY CONNECTED TO SAID RIM PORTION OF SAIDANNULAR CONTACT MEMBER, AND A DISCRETE SECOND LEAD SUPPORTING THE OTHERSIDE OF SAID CATHODE AND EXTENDING THROUGH SAID ANNULAR CONTACT MEMBERAND MOUNTED ON THE INNER SURFACE OF THE DISK-LIKE MEMBER COMPRISING ACATHODE CONTACT.